lbug 0.16.1

An in-process property graph database management system built for query speed and scalability
Documentation 
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#include "binder/binder.h"
#include "binder/expression/aggregate_function_expression.h"
#include "binder/expression/subquery_expression.h"
#include "binder/expression_binder.h"
#include "catalog/catalog.h"
#include "common/types/value/value.h"
#include "function/aggregate/count_star.h"
#include "function/built_in_function_utils.h"
#include "parser/expression/parsed_subquery_expression.h"
#include "transaction/transaction.h"

using namespace lbug::parser;
using namespace lbug::common;
using namespace lbug::function;

namespace lbug {
namespace binder {

std::shared_ptr<Expression> ExpressionBinder::bindSubqueryExpression(
    const ParsedExpression& parsedExpr) {
    auto& subqueryExpr = dynamic_cast_checked<const ParsedSubqueryExpression&>(parsedExpr);
    auto prevScope = binder->saveScope();
    auto boundGraphPattern = binder->bindGraphPattern(subqueryExpr.getPatternElements());
    if (subqueryExpr.hasWhereClause()) {
        boundGraphPattern.where = binder->bindWhereExpression(*subqueryExpr.getWhereClause());
    }
    binder->rewriteMatchPattern(boundGraphPattern);
    auto subqueryType = subqueryExpr.getSubqueryType();
    auto dataType =
        subqueryType == SubqueryType::COUNT ? LogicalType::INT64() : LogicalType::BOOL();
    auto rawName = subqueryExpr.getRawName();
    auto uniqueName = binder->getUniqueExpressionName(rawName);
    auto boundSubqueryExpr = make_shared<SubqueryExpression>(subqueryType, std::move(dataType),
        std::move(boundGraphPattern.queryGraphCollection), uniqueName, std::move(rawName));
    boundSubqueryExpr->setWhereExpression(boundGraphPattern.where);
    // Bind projection
    auto entry = catalog::Catalog::Get(*context)->getFunctionEntry(
        transaction::Transaction::Get(*context), CountStarFunction::name);
    auto function = BuiltInFunctionsUtils::matchAggregateFunction(CountStarFunction::name,
        std::vector<LogicalType>{}, false, entry->ptrCast<catalog::FunctionCatalogEntry>());
    auto bindData = std::make_unique<FunctionBindData>(LogicalType(function->returnTypeID));
    auto countStarExpr =
        std::make_shared<AggregateFunctionExpression>(function->copy(), std::move(bindData),
            expression_vector{}, binder->getUniqueExpressionName(CountStarFunction::name));
    boundSubqueryExpr->setCountStarExpr(countStarExpr);
    std::shared_ptr<Expression> projectionExpr;
    switch (subqueryType) {
    case SubqueryType::COUNT: {
        // Rewrite COUNT subquery as COUNT(*)
        projectionExpr = countStarExpr;
    } break;
    case SubqueryType::EXISTS: {
        // Rewrite EXISTS subquery as COUNT(*) > 0
        auto literalExpr = createLiteralExpression(Value(static_cast<int64_t>(0)));
        projectionExpr = bindComparisonExpression(ExpressionType::GREATER_THAN,
            expression_vector{countStarExpr, literalExpr});
    } break;
    default:
        UNREACHABLE_CODE;
    }
    // Use the same unique identifier for projection & subquery expression. We will replace subquery
    // expression with projection expression during processing.
    projectionExpr->setUniqueName(uniqueName);
    boundSubqueryExpr->setProjectionExpr(projectionExpr);
    if (subqueryExpr.hasHint()) {
        boundSubqueryExpr->setHint(binder->bindJoinHint(
            *boundSubqueryExpr->getQueryGraphCollection(), *subqueryExpr.getHint()));
    }
    binder->restoreScope(std::move(prevScope));
    return boundSubqueryExpr;
}

} // namespace binder
} // namespace lbug